"Remote function call interrupts" (CAL in /proc interrupts). What is it?

I'm running a test program which generates a large number of threads and asynchronous I/O. I'm seeing very high counts of these interrupts in /proc/interrupts, the program cannot scale beyond a certain point because CPUs are 100% saturated with softirq processing. According to: http://www.kernel.org/doc/man-pages/online/pages/man5/proc.5.html CAL stands for 'remote function call interrupt' but that's all the info I can find on google. So...what does that mean? I have smp_affinity assigned for my I/O adapter cards and those are not the CPUs taking a huge number of CAL interrupts. Is it a sign my program is running with incorrect SMP affinity?